How many years in before I should notice something though? It seems like I've been playing forever without a single event. I feel like after a few decades I should have seen something.
There isn't really a set amount of time before VIET's flavor events could fire. Basically they're generally drawn from a pool of possinle events that could fire, which includes vanillas events. In theory it's possible to go through an entire game without experiencing VIET's events, thoughu unlikely at this point given how many flavor events there are.
Anyhow one thing you can test is triggering the events yourself. Lemme see... Type "event VIETmisc.2008" into the console, it should fire an event that shouldn't effect you much (it's just a flavor event that gives 1 piety, hardly game changing). If it fires it means the events' code exists. Granted it doesn't say if the events are being triggered by the game engine, but at least they do exist.
Anyways never underestimate the RNG. I've seen some things with lottery-level chances happen, so you might just be unlucky in that regard.